Cured polyesters, properties

J.W. Cywinski, The Role of Organic Peroxides in Curing Polyester Resins and Their Influence on The Physical Properties of Re-... 

Polyester resins possess premium performance properties such as exterior durability, gloss, flexibility hardness, color stability, and versatility of cure. Polyesters are used in product finishes for household appliances, food and beverage containers, aircraft and equipment, automotive primers and bake coats, metal furniture, and fixtures. For example, water-soluble saturated polyesters are used in industrial baking paints, and in combination with melamine resin. Polyesters can be formulated in high solids and waterborne formulations to meet the requirements for the low VOC coatings being mandated by the EPA. 

The properties of cured polyesters are affected by their structural elements. These elements include the structure and ratio of acids and glycols, the type of end-group present, the type of unsaturation and the distribution of various repeating units. 

The chemical structure of glycols influences the tensile and flexural properties of cured polyester resins. Glycols with more carbon atoms generally... 

Owing to this rapid cure, a compressive strength of 40 N/mm is possible within 2 h at temperatures down to 4°C (Shaw, 1993a). The properties of polyester binder depend primarily upon the chemical composition of the polyester resin component. Typical physical properties of cured polyester binders for concrete overlays are given in Table 9.3 (ACI, 1993). 

Table 93 Typical physical properties of cured polyester concrete...

Han and Lem (1983) reviewed the cure kinetics, chemorheology and properties of curing polyester resins. 

A number of different hindered diamines have been investigated as a substitute for MOCA (1). In addition to diamine curing agents, which are used most frequently with elastomers based on polyether polyols and toluene diisocyanate (TDI), prepolymers based on polyether or polyester polyols and 4,4 -diphenylmethane diisocyanate (MDI), can be cured with diols to yield elastomers with similar properties to those of diamine-cured polyester-TDI elastomers. The most common chain extender is butanediol. However, to achieve improved mechanical properties, especially at elevated temperatures, aromatic diols are often used. The most common one is hydroquinone di-(beta-hydroxy-ethyl) ether (HEQ). 

Very little is known about the structure of the cured polyester resin. The products definitely belong in the thermoset class. There is some correlation between maximum physical properties a nd a molar ratio of 1 1 between double bonds in the alkyd and monomer. However, this is not critical and simple cross-linking does not tell the full story. The styrene monomer can be present in twice the molar amount needed, and yet complete copolymerization takes place without apparent formation of styrene polymer. 

The physical properties of a typical room temperature-cured polyester concrete is as follows Barcol hardness (50), tensile strength (500 kg cm 2), elongation (0.45%), compressive strength (1400 kg cm 2) flexural strength (1050 kg cm ) and heat deflection (41"C). The latter may be Increased by 30 by the use of fumaric acid Instead of maleic acid. 

The saturated acid (phthalic anhydride) helps to reduce the cross-link density and, hence, the brittleness of the cured polyester resin. Resin composition can be varied so that product properties can be tailored to meet specific end-use requirements. For example, a resin with enhanced reactivity and improved stiffness at high temperatures is obtained by increasing the proportion of unsaturated acid. On the other hand, a less reactive resin with reduced stiffness is obtained with a higher proportion of the saturated acid. 

Physical and thermal properties Polyesters are formed via a condensation reaction. PET and poly(butylene terephthalate) (PBT) are not crosslinked so are thermoplastic, but cured polyesters are crosslinked and thermosets. Polyesters may be reinforced with glass or carbon fibres or particles. Addition of 30% or more carbon fibre induces electrical conductivity in polyesters. Despite its high polarity, PET Is a good electrical insulator at ambient conditions because its Tg is considerably higher than room temperature. Polyesters have good abrasion resistance and are tough. PET is impervious to water but has low permeability to oxygen. 

Consider now the effect of surfactant on the properties of the initial and the cured polyester resins. Such systems show a ninnber of particular features. The structme and properties of the cured polyester resins are determined to a great extent by the compatibility of the copolymerizing components of the system. There is almost no information on the possibility of controlling this compatibility by means of surfactant, which is why it is of great interest to study the influence of surfactant upon the thermodynamics of compatibility of the components of the cured polyester resin, as well as the effect of this compatibility on the molecular mobility of the polymeric chains and on the physical-mechanical properties of the polymer. 

The influence of surfactants on the formation of microdiscontinuities. The structure and properties of the cured polyester resin are determined to a great extent by the compatibilily of the system s copolymerizing components. Let us therefore consider the possibility of regulating their compatibility with the help of surfactants. 

Properties Liq. m.w. 208.33 dec. 180 C Uses Crosslinking agent for elastomers, resins initiator for curing polyester resins finishing initiator for styrenics a synergist for some halogen-containing flame retardants polymer modifier... 

It deals with the importance, classification, materials and methods, modification, characterisation, curing, structure-property relationships and apphcations of vegetable oil-based polyesters. The chapter also includes a short review of polyesters from various vegetable oils. 

Table 2.28 Typical properties of cured polyester resins...

Unsaturated polyesters are produced via a condensation reaction between a dibasic organic acid or anhydride and a difunctional alcohol. The prepolymer is then dissolved in an unsaturated monomer, such as styrene. To initiate a cross-linking, a free radical source such as an organic peroxide is added to the liquid resin. The types and ratio of components used to manufacture the prepolymers, the manufacturing procedure, and the molecular weight of the prepolymer will determine the properties of the cured polyester. 

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